Tai McClellan Maaz

Tai McClellan Maaz
  • PhD Candidate
  • Washington State University
  • Crop and Soil Sciences


Bill Pan

Thesis or Dissertation Citation: 

Maaz, T. 2014. Nitrogen uptake and cycling by canola, pea, and wheat: implications for rotational nitrogen use efficiency. Washington State University PhD Dissertation, pp. 1-206.

Research Focus: 

N use efficiency and cycling in no-till cropping systems that feature canola, pea, and wheat

Research Abstract: 

The total soil N supply is often not factored into many N use efficiency (NUE) equations despite its high contribution to plant N nutrition and degree of internal N cycling in soil. Greenhouse, laboratory, and field experiments were conducted to determine differences in soil N uptake and partitioning in wheat (Triticum aestivum L.), field pea (Pisum sativum L.), and canola (Brassica napus L.), and their effects on net N mineralization and N carryover in soil. Multiple nitrogen recovery indices were utilized to track N in the various systems, including the recovery of 15N fertilizer by crops, N uptake efficiency, available N uptake efficiency, apparent fertilizer N recovery, net N mineralization, apparent N mineralization, rotational NUE, rotational N uptake efficiency, and rotational N utilization efficiency. Results from the greenhouse study highlighted the importance of soil derived N supply, which was taken up proportionately more than fertilizer N. The laboratory experiment linked the partitioning of C and N into structural and soluble cell components to the net N immobilization potential of soil. Findings from the field study related the contribution of N carryover and residue N to the N availability of subsequent crops and to enhanced N uptake and recovery efficiencies. Multi-year N balances adequately captured effects of fertilization and inclusion of legumes on increased subsequent N availability and rotational N v use efficiencies. Finally, a case study is presented, which examines the driving forces for canola adoption, key factors leading to adoption, and institutionalized programs and organizations that sustain the canola industry in Canada and Australia. Initial public investments in research and market development, competitive prices, and the release of high yielding adapted varieties with advanced agronomics were instrumental for the development of a viable canola industry. The results from these studies will inform Washington growers of agronomic, ecological, social, economic, and political considerations when introducing canola production into wheat-based cropping systems.


I was born and raised Southwest Virginia. I received BS and MS degrees in Soil Science from the University of Hawaii at Manoa. My research is also funded by WSU's Nitrogen System's: Policy-oriented Integrated Research and Education (NSPIRE) and Washington State Biofuel Cropping System (WBCS) programs, and I was a recipient of the 2013 International Plant Nutrition Institute Scholar Award. During my research endeavors, I have developed an interest in data management, analysis, and visualization. I hope to explore these disciplines with a focus on agricultural science in the future.

Publications and Presentations: 

Pan, W., Maaz, T., Hammac, W., McCracken, V. Koenig, R. 2016. Mitscherlich-modeled, semi-arid canola nitrogen requirements influenced by soil nitrogen and water. Agronomy Journal. 108(2): 884-894.
Maaz, T., Pan, W., Hammac, W. 2016. Influence of soil nitrogen and water supply on canola nitrogen use efficiency. Agronomy Journal. 108(5): 2099-2109.